text: In the late 1960s, Orgel proposed that life was based on RNA before it was based on DNA or proteins. His theory included genes based on RNA and RNA enzymes. This view would be developed and shaped into the now widely accepted RNA world hypothesis.
  Almost thirty years later, Orgel wrote a lengthy review of the RNA World hypothesis. This review highlighted many proposed syntheses for RNA and its parts in abiotic conditions, noted the significance of the discovery of ribozymes (RNA molecules that function as enzymes just as Orgel had once predicted) and at the same time, demonstrated nucleic acid polymers with alternatives to ribose such as threose nucleic acid (TNA) and peptide nucleic acid (PNA).
  In conclusion, Orgel wrote, "One must recognize that, despite considerable progress, the problem of the origin of the RNA World is far from being solved."